2010 technological studies standard grade – credit

©

2010 Technological Studies

Standard Grade – Credit

Finalised Marking Instructions

© Scottish Qualifications Authority 2010

The information in this publication may be reproduced to support SQA qualifications only on a non-

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secondary sources.

These Marking Instructions have been prepared by Examination Teams for use by SQA Appointed

Markers when marking External Course Assessments. This publication must not be reproduced for

commercial or trade purposes.

Mark Allocation Marks

KU RNA

1. A manufacturer wants to use a cruise control system to keep a car’s speed constant even when it

goes up and down hills. The system should allow a driver to take their foot off the accelerator

once the desired speed has been set.

(a) Complete the control diagram below for the cruise control system.

2

1

0

(b) State the name of the control diagram symbol X.

1

Error detector KU 0

(c) This control system makes use of a feedback loop. State the type of control produced

by this automatic system.

1

Closed loop KU 0

Desired Speed

or Set Level

Constant

Speed

Speed sensor/

Tachogenerator

+ -

X

Control

Unit Engine Wheels

RNA

RNA

Marks

KU RNA

2. An interior designer wants three lamps to come on when a switch is activated. The lighting

circuit is shown below.

(a) State two reasons why it is good practice to have the lamps wired in parallel rather than

in series.

(i) Other remains lit if one breaks KU

(ii) Easy to spot the faulty lamp/be brighter KU

(b) Calculate, showing all working and units, the total resistance of the lighting circuit shown

above.

tR

1 =

1R

1 +

2R

1 +

3R

1

=

100

1 +

100

1 +

60

1 RNA substitution

= 0·0367 2

1

Rt = 27·27 Ω RNA correct answer from given working 0

The designer wants the brightness of the lights to be altered using the following component.

(c) State the name of the component shown above.

1

Variable resistor KU 0

(d) State the name of the device that is used to measure current in a circuit.

1

Ammeter KU 0

100Ω 100Ω 60 Ω

230 V

2

1

0

Marks

KU RNA

3. A geothermal power plant uses the heat in the earth to help produce electricity.

(a) Calculate the heat energy absorbed by 100 litres of water which is pumped into the earth

at 10°C and comes out as steam at 240°C. (1 litre of water has a mass of 1 kg.)

E

h = mc T Δ

= 100 × 4190 × 230 RNA substitution

RNA temperature change

Eh = 96370000 J 3

2

= 96.37 MJ RNA correct answer from given working 1

0

(b) For every 15 MJ of heat energy that comes from the ground, the power plant produces

5·34 MJ of electricity.

(i) Calculate the efficiency of the power plant.

η = Useful energy out × 100%

Total energy in

15MJ

34MJ5 ⋅ RNA substitution =

2

= 35·6% RNA correct answer from given working 1

or 0·356 0

(ii) Explain why a system, such as the power plant, will not be 100% efficient.

1

Energy is lost during production etc 0

Marks

KU RNA

3. (continued)

(c) Geothermal is a source of renewable energy. State two other examples of a renewable

energy source.

1 Solar, tidal, biomass, wind

KU each (max 2)

2 hydro(electric) etc

(d) State two disadvantages of using fossil fuels, other than cost.

1 Pollution

KU each (max 2)

2 Dwindling supply etc

(e) State two ways that energy can be conserved in the home.

1 Insulation

KU each (max 2)

2 Switching off unused appliances etc

2

1

0

2

1

0

2

1

0

Marks

KU RNA

4. A test rig in a furniture factory is operated by the pneumatic circuit shown below.

Valve 3

Valve 4

RNA

(d) (ii) X

Valve 2

To on/off

switch

Y Valve 1

(a) Describe, using appropriate terminology, how the pneumatic circuit operates.

When Valve is actuated....main air flows to valve 2 then causes the DAC to

outstroke. When fully outstroked it actuates valve 4 sending a pilot signal

towards valve 2. After a delay valve 2 actuates causing the DAC to instroke. This

actuates valve 3 which sends a pilot signal to valve 2 causing it to change state and

5

4

outstroke the piston. The sequence repeats until valve 1 is no longer actuated. 3

2

1 RNA for each valid point up to a maximum of 5

1

0

Marks

KU RNA

4. (continued)

(b) State the full name of the following components.

Valve Solenoid/Spring Return/3/2 valve for each part

1

Component Y Reservoir KU 0

(c) State two ways to vary the length of a pneumatic time delay.

1 Adjust the restrictor KU

2 Change the volume of the reservoir KU

To reduce damage it was decided to slow the piston movement as it outstrokes. The piston

should still instroke quickly.

(d) (i) State the full name of a pneumatic component that could be used to slow a piston

in one direction.

1

Uni-directional restrictor KU 0

1

(ii) Mark (X) on the pneumatic circuit where this component should be inserted. 0

(e) State the name of the following pneumatic actuators.

2

1

Lever KU Diaphragm KU 0

KU

3

2

1

0

2

1

0

Marks

KU RNA

5. A prototype circuit for a parking sensor in a car is shown below.

12 V + 5 V

Z

2 k Ω

1 kΩ

Vout

0 V

(a) (i) State the name of component Z shown in the circuit above.

1

KU Buzzer 0

(ii) State the type of relay shown in the circuit above.

1

KU Single Pole Single Throw (SPST) 0

(b) Describe the operation of the circuit.

As light level drops the resistance of the LDR increases and V out

increases. When Vout is at the appropriate level (0·7 V) the transistor

3

2

switches on. This causes the relay to turn on and the buzzer to sound. 1

0

RNA for each valid point up to 3 marks

(c) Calculate, with reference to the Data Booklet, the value of Vout when the light level on the

LDR is 9 lux.

RNA correct value from Data Booklet From the Data Booklet, R ldr = 10 kΩ

T

1

R

RVout = × Vs

RNA substitution

= 12000

10000 × 5 3

2

1

RNA correct answer from given working

Allow FTE

= 4·167 V 0

Marks

KU RNA

5. (continued)

(d) State the voltage at which a transistor saturates.

1

0·7 V KU 0

(e) A diode is normally wired in parallel across devices such as relays. State the purpose of

the diode.

1

To protect the transistor KU 0

Marks

KU RNA

6. A music venue has a system to cut off the power supply if a band plays too loudly.

The system is operated by a microcontroller.

A flowchart for the control system is shown below.

Start

Initialise

No Is music too loud?

Yes

Warning light on

0·5 second delay

Warning light off

0·5 second delay

No Has this been

done 10 times?

Yes

No Is music too loud?

Yes

Shut off power

Stop

Marks

KU RNA

6. (continued)

Input and output connections to the microcontroller are shown in the table below.

Input Connection Pin Output Connection

7 Power supply shut off

(1 = shut off, 0 = power on)

6 Warning light

5

4

3

2

1

Sound sensor

(1 = loud, 0 = quiet)

0

Complete, with reference to the flowchart, Data Booklet, and the input/output connections,

the PBASIC control program.

init: let dirs = %11110000 ‘set pins 7-4 as outputs, rest inputs

let pins = 0 ‘all pins off

symbol counter = b0 ‘define counter address b0

main: if pin0 = 0 then main ‘if sound level is quiet then jump to main

‘set for … next loop to 10

for counter = 1 to 10 RNA

high 6 RNA

pause 500

RNA low 6 RNA

for both pause 500

next counter RNA

if pin0 = 0 then main RNA

high 7 RNA

end RNA

8

7

6

5

4

3

2

1

0

Marks

KU RNA

7. Part of an electronic circuit used to control a central heating system is shown below.

+ Vcc

7432 7408 7404

A-Temperature Z-Boiler Sensor

B-Timer

C-Test switch

0 V

(a) Complete, with reference to the Data Booklet and the wiring diagram, the logic diagram

for the central heating system.

RNA

6

5

4

3

2

1

0

RNA for each gate A

B Z

C

RNA RNA

Marks

KU RNA

7. (continued)

(b) TTL Integrated Circuits (ICs) are used in the prototype but CMOS ICs are chosen for the

final product.

State two advantages of CMOS ICs over the TTL ICs.

1 Low power consumption, high fan out, 2

1

2 various power supplies etc KU each up to 2 0

(c) An engineer designed and tested the circuit using a computer simulation.

State two reasons why new circuits are often tested on a computer first.

1 Easier to change, no faulty components, 2

1

2 quicker to construct etc KU each up to 2 0

(d) The engineer assembled the circuit on a breadboard and used an LED to show a high

output.

(i) State the full name of an LED.

1

Light Emitting Diode KU 0

(ii) Draw the symbol for an LED below.

1

0

KU

Marks

KU RNA

8. A simplified diagram of a microcontroller system is shown below.

(a) (i) State the full name of the following microcontroller sub-systems.

I/O PORT Input/Output port KU

EEPROM Electronically Erasable Programmable

Read Only Memory KU

(ii) Describe the difference between RAM and ROM.

RAM is a temporary form of storage, data lost when power

switches off etc

ROM is a permanent form of storage, cannot be changed etc 2

1

KU for each correct description (1 of each) 0

(b) (i) State the name of the connections that are used to transfer data from one

microcontroller sub-system to another.

1

Bus (buses) KU 0

(ii) Describe the function of the ALU.

1

Does all internal calculations, processes data KU 0

(c) (i) Convert the following binary number to decimal.

1

%10001011 139 RNA 0

(ii) Convert the following decimal number to binary.

1

102 % (0)1100110 RNA 0

RAM EEPROM ROM

ALU

CLOCK

I/O Port

Program

External

devices

2

1

0

Marks

KU RNA

9. A model train climbs a steep slope at an amusement park.

A simplified diagram of the train drive system is shown here.

32 teeth 2000 rev/min

80 teeth

25 teeth

Part X – 90 teeth

Part Y

(a) State the names of the labelled parts of the drive system in the diagram above.

KU Pinion Part X

2

KU Part Y Rack KU

1

0

(b) A simplified diagram of the train drive system is shown. Calculate the speed of the

90 tooth gear. 32 teeth 2000 rev/min

80 teeth 25 teeth

RNA 90 teeth

Part X

⎟⎠⎞

⎜⎝⎛×⎟

⎠⎞

⎜⎝⎛

90

25

80

32 RNAOutput Speed = 2000 × RNA substitution

= 222 rev/min RNA correct answer from given

working

OR

Speed80T = 2000 × 32/80 = 800 rev/min RNA correct answer from given

working

RNA substitution

4

Speed90T = 800 × 25/90 = 222 rev/min RNA correct answer from given

working

3

2

1 RNA substitution 0

Marks

KU RNA

9. (continued)

(c) Calculate the linear speed of the train along the track. The pitch of Part Y is 50 mm.

Part X

90 teeth Part Y

50 mm

Speed = pitch × revs × teeth

= 50 × 222 × 90 RNA substitution (allow FTE)

2

= 1000000 mm/min RNA correct answer from given working 1

999000 mm/min 0

(d) State the names of the mechanisms below.

KU nut (i) Worm and

2

ignore order

(ii) Worm and wheel KU 1

0

(iii) State an advantage in the use of a worm in a lifting system.

1

KU No overhaul, large speed change between input and output etc 0

increase torque

Marks

KU RNA

10. A microcontroller operates the motors in a robotic dog. To

make the dog move in a life-like way the motors must be able

to turn at a slower speed.

(a) Describe, with the aid of a sketch, or sketches, how a microcontroller program can be

used to make a motor turn at a slower speed.

Normal Slower

KU for mark and space correctly identified or defined

3

KU for pulsed signal drawn or defined, or PWM stated 2

KU for describing or drawing a changing ratio of mark and space

for slowing

1

0

To reduce damage to the robotic toy the program uses a “soft start” technique when operating

the motors. The “soft start” is illustrated in the diagram below.

The diagram below shows the output signal to the motor.

1

0 time

(b) Describe, with reference to the diagram, what will happen to a motor when the “soft

start” is used.

1

The motor will gradually speed up 0

[END OF MARKING INSTRUCTIONS]

2010 technological studies standard grade – credit

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